Measuring sensors of the kind described above are known from U.S. Pat. No. 3,767,552. The measuring characteristics of these measuring sensors are essentially determined in that the diffusion membrane remains in close proximity to the metallic supporting body configured as an electrode and from which the measuring signals are transmitted to an evaluation unit. For this purpose, complex clamping and sealing measures are necessary whereby the membrane applied to the supporting body is clamped thereover. In addition, an adequate seal of the electrolyte chamber with respect to the remainder of the measuring sensor housing must be provided for the assembled condition. In this connection, it is noted that the membrane cannot be expanded too greatly during the clamping process so that its diffusion characteristics for the gas component to be detected is not changed in an unwanted manner or that capillary-like expansion fissures are formed from which the electrolyte can escape unnoticed during storage or operation. Measuring sensors of the above kind operate in the so-called diffusion limited current region. For this reason, the signal quality is essentially dependent upon the following: the diffusion characteristic of the membrane for the gas component to be detected, the electrode structure and the coaction of the membrane and measuring electrode. It is desirable to select the diffusion membrane as a diffusion barrier which is as thin as possible and made of a material having a good diffusion constant in order that the shortest possible response time for the measuring sensor can be achieved when there is a change in the gas concentration. The handling of such an extremely thin membrane is especially difficult and the sealing measures are most complex especially during installation of the membrane.
A further disadvantageous influence on the measuring signal is caused by the condition that the membrane applied to the support body forms regions between the membrane and the support body wherein electrolyte liquid enters when the membrane is clamped in place. The electrolyte liquid takes up the reaction product from the conversion of the gas component to be detected, but a subsequent removal of this reaction product and a replacement with fresh electrolyte liquid is impeded. This leads to defective measurements as a consequence of the changing transport coefficients of the components in the electrolyte which participate in the reaction. In addition, electrolyte regions can form between the membrane and support body which participate in the gas exchange through the membrane but for which a long diffusion path in this electrolyte region is present for the reaction at the electrode. This leads to an increase of the response time and to a delayed adjustment of the stable final measurement value.
Special manipulation difficulties are associated with arrangements having membranes coated on one side with a conductive coating such as by means of a sputtering operation. This process does not lead to an especially good adherence capability between membrane and coating which becomes noticeable especially with the necessary introduction into the arrangement and impregnation with the electrolyte. Often, the coating separates from the membrane so that a close proximity of the coating to the membrane is no longer ensured. This increases the rejection of unsuitable gas-measuring cells in a production process which is already complex. Also, the manipulation of such sputtered membranes is quite problematical since stresses are generated in the membrane because of the sputtering and these stresses make an attachment free of folds difficult during further handling.